1. Field of the Invention
The present invention generally relates to an acrylic composition. More particularly, the present invention relates to an acrylic composition that can be incorporated into a curable coating composition and then used in coating applications, such as an automotive coating application, to produce films that have suitable scratch, mar, and chip performance.
2. Description of the Related Art
Acrylic compositions and their use in a wide variety of coating applications are known in the art. In a curable coating composition, acrylic compositions, along with a suitable cross-linking agent, generally produce a film having good film properties, such as resistance to scratch, mar, and chip. Curable coating compositions that utilize acrylic compositions typically require solvents to dissolve or otherwise reduce the acrylic composition for processing and application purposes. Solvents are required primarily due to a high molecular weight and a correspondingly high viscosity for the acrylic composition.
Although the conventional acrylic compositions are generally inexpensive to prepare, these particular compositions with large proportions of non-functional alkyl acrylic monomers provide poor recoat adhesion due to the formation of pendant and non-functional acrylic chains during cure. These acrylic chains migrate toward an upper surface of a cured film of a coating composition having the conventional acrylic composition and inhibit the adhesion of coating compositions that are subsequently applied to the cured film. It is also known in the art that other properties of the cured film, including scratch and mar resistance, may be compromised when the coating composition includes the conventional acrylic composition due to the formation of the acrylic chains described above. Furthermore, the conventional acrylic compositions that do not include carbamate functionality for subsequent cross-linking with aminoplasts exhibit poor resistance to acid etch. As a result, cured film formed from the conventional acrylic compositions is susceptible to damage due to acid rain.
It is known that there is a movement toward utilizing acrylic compositions that have lower molecular weights so as to reduce the overall amount of solvents, i.e., volatile organic compounds (VOCs), required in the coating composition. However, it is also known that coating compositions that utilize conventional acrylic compositions with lower molecular weights produce films that have poorer film properties as evidenced by decreased scratch, mar, and chip performance.
Highly branched, e.g. star, compositions are being utilized more frequently because they offer higher molecular weights yet they exhibit low viscosity, as compared to the viscosity of conventional acrylic compositions, i.e., acrylic compositions that are not highly branched. These highly branched compositions have, to date, primarily been polyester-based. However, some highly branched acrylic compositions have been developed by complex methods such as Atom Transfer Radical Polymerization (ATRP) and Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization. These methods are complex, and are therefore generally undesirable for a variety of reasons including, but not limited to, slow reaction times, poor manufacturability, use of metal or sulfur-containing compounds, and a requirement for post purification of the acrylic composition.
Due to the inadequacies associated with the acrylic polymers of the prior art, especially the highly branched acrylic compositions developed by ATRP and RAFT, it is desirable to provide a novel acrylic composition that is economical and highly-branched. It is also advantageous to provide an acrylic composition, and a curable coating composition including the acrylic composition, that promotes acid etch resistance, enhances recoat adhesion, and is optimized for cross-linking when used in coating compositions.